I suspect you've already put MORE thought in on the issue than the film makers ever did....They changed it because using the same jacket is "boring", I suspect......Hugh Jackman's lead on the Wolverine movies is probably what resulted in them using the design they used for Origins, since it matches the X1 close enough to provide a link, but there's clearly no overall link to what they choose, outside of a rough idea...They chose one design, changed it slightly each movie, and then Origins attempted to show that there WAS a link...
Wolverine also would have more than one jacket, seeing how treats them...LOL...I can see the 70's version being used early on with the X0 coming in for the 80's and then being stuck with in essentials for the rest of the time, until X Men 3.....That makes about as much sense as we're likely to get on the subject I reckon...